1. Field of the Invention
The present invention relates to a composite product having improved properties formed from cellulose, and a method of producing the same.
2. Description of the Prior Art
Cellulose is a structural polysaccharide, which is the main component of the cell wall of a higher plant and makes up ⅓-xc2xd of the plant body. Cellulose is the most abundant organic compound on the earth.
Due to the strong hydrogen bonds between the hydroxyl groups, cellulose exhibits high crystallinity between the aligned main chains. Cellulose is a polymeric compound which does not show thermoplasticity. Cellulose is derived from plants and also produced by microorganisms. Cellulose produced by microorganisms is bacterial cellulose. The solubility of the plant-derived cellulose in a solvent is improved by treatment with an alkali or by introducing a soluble substituent. The resulting solution is poured into a mold having a desired shape and the solvent is removed to give a molded product of the cellulose. To form bacterial cellulose, xanthan gum is added to a culture medium for cellulose-producing bacteria to control the crystal structure of the bacterial cellulose, as has been reported in Japanese Patent Laid-Open No. 6-206904. Further, a method of forming a sheet material having high mechanical strength is conducted by applying pressure and heat to the bacterial cellulose film comprising ribbon-like microfibrils produced by cellulose-producing bacteria, as reported in Japanese Patent Publication No. 8-32798. Also, a so-called powder molding method is known in which cellulose in the form of a fine powder is pressurized and heated.
Recently, as the environmental problems and resource problems have become more serious, cellulose has become popular again since it has biodegradability, and is a resource which can be regenerated in nature. However, cellulose is not soluble using conventional solvents and is not deemed appropriate for film applications requiring cellulose solutions. When dissolved in a special solvent such as copper-ammonia solution and the like, a molded cellulosic product, such as a film, can be produced by a solvent method, but the molded product obtained in such a method is rather poor in flexibility and its quality is unacceptable for practical use. In addition, since cellulose does not exhibit thermoplasticity, it has been very difficult to produce a thermoformed article by the hot-press method.
In view of the above-mentioned technical background, the prevent invention provides a cellulosic composite product whose processability is far more improved than a cellulose with the biodegradability, the original property of cellulose, intact. The present invention also provides a method of producing a cellulosic composite product whose processability is improved while maintaining the original biodegradability.
According to a first aspect of the present invention, there is provided a cellulosic composite product which can achieve the above-mentioned object which comprises cellulose and a compound represented by the following formula (I); 
wherein, R represents a substituted or unsubstituted alkylene group or a substituted or unsubstituted arylene group, G represents a monosaccharide residual group or an oligosaccharide residual group and n is degree of polymerization and is an integer between 1 and 5000.
According to another aspect of the present invention, there is provided a method for producing a cellulosic composite product comprising the steps of: providing a liquid containing dissolved or dispersed cellulose and a compound represented by the following formulae (I); 
wherein R represents a substituted or unsubstituted alkylene group or a substituted or unsubstituted arylene group, G represents a monosaccharide residual group on an oligosaccharide residual group and n is an integer between 1 and 5000; and evaporating the liquid by heating.
According to further aspect of the present invention, there is provided a process for producing a composite product comprising culturing cellulose-producing bacteria in a culture medium containing a compound of formula (I) 
wherein R represents a substituted or unsubstituted alkylene group or a substituted or unsubstituted arylene group, G represents a monosaccharide residual group or an oligosaccharide residual group and n is an integer between 1 and 5000; and making the bacteria produce cellulose.
In addition, the invention includes the composite product is formed by interacting cellulose and the compound of formula (I) above. Further the invention also includes the composite product produced by providing a liquid containing dissolved or dispersed cellulose and a compound of formula (I) above and then evaporating the liquid by heating. Further, the invention encompasses the composite product produced by culturing cellulose-producing bacteria in a culture medium containing a compound of formula (I) above and then making the bacteria produce cellulose.
In general, it is believed that the poor processability of cellulose is caused by its high crystallinity. This high crystallinity is believed derived from strong hydrogen bonds between the main chains of the microfibril structure of cellulose which become aligned. The inventors believe that the similarity"" in structure between cellulose and the monosaccharide or oligosaccharide derivative represented by formulae (I) permits good bonding capacity between the compound of formula (I) and cellulose. In other words, the compound of formula (I) has good affinity with cellulose. The composite product of the formula (I) compound and cellulose is characterized by an intermolecular-interaction between the two compounds and exhibits far better processability than cellulose. A molded product made of the composite product has good mechanical strength and flexibility.
The exact reason why the present composite product provides the aforementioned beneficial properties is still unknown, but it may be attributable to the structure of the compound of formula (I). That is, the compound of formula (I) has a similarity to cellulose in structure, particularly in the sugar moiety (G) having a hydroxyl group, and a dissimilarity to cellulose in the alkylene or arylene moiety (R). The moiety (G) may act to express an affinity to cellulose on the one hand, while on the other hand, the moiety (R) contained in the structure in a certain ratio, does not form any hydrogen bonds with cellulose and may act to reduce the high crystallinity of cellulose.